They will light your path in dark dungeons and caves.
Wisps are equitable, so you can assign them to hotkey.
Wisps will give you useful magic effects while wearing them
Your followers can equip wisps as well.
If you are using "Frostfall" wisps will provide warmth.
Wisp behavior is customizable via settings menu, you can set automatic or manual mode.
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How to:

Once you install mod, quest will be initiated, that will lead you to Ruins of Rkund. There you will find book in the chest. Read it and you'll get magic ability to craft unique dwarven wisps and fill them with light.
You can craft them on blacksmith anvil under misc category. You'll need some resources like dwarven oil, gold ingot, flawless garnet and etc.
For lazy persons: There is a cheat urn in Riverwood Sleeping Giant Inn.

known issues:

If you are using multiple follower mods, beware to summon too many wisps together, large amount of lighting may cause light flickering and even desktop crash

Requirements: None

Compatibility: There shouldn't be any conflicts, unless with mods that use same armor slot (59). (tip: you can always change slot in SSE edit)